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I have some questions about von Weizsäcker's views in physics, which I find them generally interesting. One of them is that he thought that time was fundamental (he even thought that logic, which is atemporal, was derived from a more fundamental temporal logic). He thought that time was a fundamental characteristic of physics and quantum mechanics in particular.

My question is: Do you know if von Weizsäcker changed his mind towards time being fundamental or if he eventually considered quantum models in which time was not fundamental?

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Weizsäcker did not change his mind and continued to develop "temporal logic" until 1990-s (e.g. in Zeit und Wissen, 1992). It is central to his general idea of the relationship between logic and physics inspired by Kant's idea that time is a precondition of experience of events/phenomena. Weizsäcker's views were quite distinct from then (and even now) common interpretations of quantum mechanics, as Stöckler pointed out:

"His approach is not any longer present in contemporary debates. One reason is that Weizsäcker is mainly affected by classical philosophy (Plato, Aristotle, Kant). He could not esteem the philosophy of science that was developed in the spirit of logical empiricism. So he lost interest in disputes with Anglo-Saxon philosophy of quantum mechanics."

In some respects, already back in 1950-s Weizsäcker anticipated what is now called quantum information approach. He even had an analog of qubits, called urs, that served as 'elements of reality', not unlike Wheeler's later "it from bit", see Are Wheeler's It from Bit/Participatory Universe and the Multiverse related? Moreover, according to Weizsäcker, the ordinary logic deals with structural, timeless ("time-bridging") propositions, while physics deals with contingent ones. The temporal logic is supposed to give a more fundamental description that both of them derive from, see Görnitz and Ischebeck, Introduction to Carl Friedrich von Weizsäcker's Program for a Reconstruction of Quantum Theory:

"In Komplementarität und Logik, a "logic of complementarity" is abstracted from quantum theory whose core is Birckhoff and v. Neumann's quantum logic [1]. It is understood as the physical quantum theory, expressed as a logical formalism... Weizsäcker went on to design a "temporal logic" which would be the common basis of logic, as the theory of time-bridging propositions and schematic proofs, and of physics, as the theory of predictions and empirical decisions... Weizsäcker reports on his work in logic in Aujbau der Physik [19] and Zeit und Wissen [20].

The papers on Komplementarität und Logic introduce the ur, the quantized binary alternative and quantum bit of information, as the basic concept in the reconstruction. The ur-hypothesis was formulated that particles and fields, as well as space can be built from urs. This means a construction of matter and fields out of quantum information... Weizsäcker, however, gives binary alternatives a basic physical significance. Physical objects should be built from urs. The ur-hypothesis follows the rule that mathematical objects of physical theory should be representative of physical objects as much as possible".

For more details on the temporal logic see Drieschner, Is (quantum) logic empirical?

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  • $\begingroup$ thatnk you for your help again. So that means that Weizsäcker never considered models where logic was fundamentally non temporal? @Conifold $\endgroup$
    – vengaq
    Mar 3, 2020 at 19:46
  • $\begingroup$ @vengaq He "considered" classical logic, of course, he just thought that the more fundamental theory had to include time in some form to account for "events", which he believed were needed to make sense of quantum probabilities. $\endgroup$
    – Conifold
    Mar 3, 2020 at 19:54

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